Prior art flexible hollow waveguide for transmitting coherent CO2 laser radiation described by Katherine D. Laakmann (U.S. Pat. No. 4,652,083) defines a hollow tube having both metal and dielectric layers on its inner surface. First layer on the inner surface of the hollow tube is a highly reflective metal coating. Second layer on top of reflective metal coating is the dielectric coating having its thickness chosen to enhance the reflectivity for both polarizations of the transmitted laser light at the wavelength desired. However, U.S. Pat. No. 4,652,083 did not describe a suitable manufacturing method to produce an inexpensive, durable and efficient hollow waveguide fiber. A particular problem in creating a commercially viable hollow waveguide fiber is forming a highly reflective metal layer (preferable gold, silver, copper or aluminum) on the inner surface of the small diameter tube, which is preferably made of metal, e.g. stainless steel, for durability and ruggedness. Typical metal coating techniques onto metal substrates involve electro-plating, which is not feasible inside of a small diameter (typically 1 mm or less) and long (typically 1 m or more) stainless steel tubing. Another prior art design (U.S. Pat. No. 4,913,505 by Michael B. Levy) has successfully overcome these manufacturing problems by depositing required metal and dielectric layers onto ribbon shaped substrate prior to forming a hollow waveguide. U.S. Pat. No. 4,913,505 defines a lightpipe, which is formed by rolling an elongated ribbon into an elongated tubular structure already having highly reflective coating on its inner surface. However, this design has an intrinsic disadvantage of light scattering/absorbing seam extending the whole length of the finished hollow waveguide fiber.
Another prior art hollow waveguide fiber design by Natan Croitoriu et. al. (U.S. Pat. No. 4,930,863) defines metal layer of silver deposited on the inner surface of the hollow glass or dielectric tube using well known glass mirror silvering techniques. Once the silver layer is formed, then silver iodide Agl dielectric layer can be formed by iodizing the silver Ag layer. Such design and method was further significantly improved by James A. Harrington et. al. (U.S. Pat. Nos. 5,440,644 and 5,567,471) by using fused silica tubing with its highly polished inner surface. A particular disadvantage of glass and fused silica hollow waveguide fibers, particularly in commercial medical applications, is a necessity to employ rugged and often expensive jacketing around the fiber to facilitate safe and secure usage of such fibers. Another prior art hollow waveguide fiber design by Clifford E. Morrow et. al. (U.S. Pat. No. 5,325,458) utilizes a very simple design having a hollow silver Ag tube having its inner surface chemically polished and then chemically treated to create silver halide (AgBr, AgCl or Agl) dielectric layer. However, disadvantage of such design is due to relative softness of the silver tubing and necessity to employ rugged and often expensive jacketing around the fiber to facilitate safe and secure usage of such fibers.
It is an object of the present invention to provide an efficient design and method for manufacturing an inexpensive, durable and rugged metal tube hollow waveguide fiber having seamless light guiding inner bore surface.
It is an another object of the present invention to provide an efficient design and method for manufacturing an inexpensive, durable and rugged metal tube hollow waveguide fiber having seamless silver (Ag) and silver halide (Agl, AgBr or AgCl) plated light guiding inner bore surface.
Still yet another object of present invention is to provide an efficient method for eliminating light scattering/absorptive seam inside of the ribbon-formed hollow waveguide fiber by forming a seamless light-reflective layer over the inner surface of the ribbon.